The present invention relates to a hydraulic control device with a first hydraulic actuator, which actuator has a housing containing a cylinder space in which a piston/piston rod assembly is accommodated in such a way that it can move axially to and fro between corresponding first and second end positions, which piston/piston rod assembly projects out of the housing.
In the cylinder space the piston/piston rod assembly bounds a first chamber and second chamber, which chambers have a volume that depends on the position of the piston/piston rod assembly, the volume of the first chamber being at its smallest if the piston/piston rod assembly is situated in the first end position, and the volume of the second chamber being at its smallest if the piston/piston rod assembly is situated in the second end position.
The housing is provided with a first and a second connection for the supply and discharge of hydraulic fluid, which connections are in communication with the first and the second chamber respectively by way of a first and a second opening respectively in the cylinder space.
The control device is provided with damping means for the purpose of producing a damping of the movement of the piston/piston rod assembly near the second end position.
A hydraulic control device is known, for example from the applicant""s EP 1 031 697.
In the case of this known control device the first hydraulic actuator is provided with a bypass channel, along which fluid supplied to a chamber of the hydraulic actuator can flow fully or partially away if the piston has cleared the inflow opening of the bypass channel. The bypass channel produces the effect that the speed of movement of the piston/piston rod assembly is damped before the end position is reached. The power that can be delivered by the hydraulic actuator also decreases as soon as fluid supplied under pressure to a chamber of the actuator can flow away by way of the bypass channel.
In practice, it happens that damping of the speed of movement of the piston/piston rod assembly is desirable, but that it is a problem that the power that can be delivered by the actuator decreases already before the end position has been reached.
The object of the present invention is to provide an improved hydraulic control device, by means of which, on the one hand, a good damping action can be obtained and, on the other hand, the actuator can continue to deliver power effectively until it reaches its end position.
The present invention achieves the abovementioned object by providing a hydraulic control device which is characterized in that the damping means are achieved by the fact that the piston/piston rod assembly is provided with shut-off means, which are designed in such a way that during movement of the piston/piston rod assembly from the first to the second end position they shut off the second opening of the cylinder space before the piston/piston rod assembly reaches the second end position, and by the fact that the first hydraulic actuator is further provided with a third connection, which by way of a third opening is in communication with the second chamber in any position of the piston/piston rod assembly, and by the fact that the hydraulic control device further comprises a throttling facility, which is connected to the third opening, for the purpose of controlling the volume flow of hydraulic fluid out of the second chamber if the second opening has been shut off by the shut-off means.
By means of the invention it is ensured that, during movement of the piston/piston rod assembly to the second end position, at a particular moment before said end position is reached the shut-off means shut off the second opening. As a result of this, the fluid from the second working chamber can now flow out only by way of the third opening and the throttling facility connected to it.
Said throttling facility limits the outflow velocity, so that the movement of the piston/piston rod assembly near the second end position is a damped movement.
The throttling facility is preferably a flow-regulating valve.
The solution according to the invention is particularly advantageous in the case of a hydraulic actuator of small diameter, in the case of which during the damping action of the actuator very small fluid volumes flow out of the second chamber. A flow-regulating valve produces a stable outflow in the case of small volumes.
In practice, it often happens that a movable part, for example a movable part of a vehicle, such as, for example, a vehicle hood assembly for covering a passenger space of the vehicle, or a vehicle boot cover, is driven by two hydraulic actuators, disposed on opposite sides of the part in question.
In that situation provision is preferably made for the hydraulic control device further to comprise a second hydraulic actuator, which is of an entirely conventional design. The damping action is therefore present in the case of the second hydraulic actuator, without any separate facility being necessary for that actuator. This is very advantageous technically and from the point of view of cost.
The throttling facility is preferably a pressure-compensated flow-regulating valve, so that the damping action obtained is substantially independent of the temperature, viscosity and pressure of the outflowing fluid. The flow-regulating valve is preferably of an adjustable design.
The invention will be explained in greater detail below with reference to the drawing.